Multiple flour bleaching process



June 20, 1944.

Original Filed Aug. 16-1940 Patented June 20, 1944 MULTIPLE FLOUR BLEACHING PROCESS Charles G. Ferrari, Minneapolis, and Willis S. Hutchinson, St. Paul, Minn., assgnors to General Mills, Inc., a corporation of Delaware Original application August 16, 1940, Serial No. 352,910. Divided and this application May 10. 1943, Serial No. 486,444

2 Claims.

'Ihe present invention relates to the improvement oi wheat ilour and other edible iinely divided milled products, including the color, baking,

.and keeping qualities thereoi and more particularly has reference' to processes for the bleaching and aging or maturing of our and the like.

This application is a division of our copending applicatiomserial No. 352,910, iiled August. 16, 1940.

The principal object of our invention is to 'pro-l Ivide a process for the production oi a bleached flour of excellent'color without either adversely aiecting its baking vproperties orv its keeping qualities.

Another object of our invention is to provide a bleaching process for our and the like in which smaller quantities of bleaching agents are required for the bleaching and maturing operation than would be required according to the usual commercial bleaching methods.

A- further object oi our invention is to provide a bleaching process for flour and the like which will enable baked goods of greater volume to be produced from the iiour bleached by ,our process than would be produced from flour bleached by conventional bleaching methods.

A still further object of our invention is to provide a process for the multiple bleaching and maturing oi' wheat ilour and other edible finely divided milled products which comprises exposing our or other nely divided products while agitated in a iinely divided state to the action oi a gaseous bleaching agent for a'suillcient length of time and ata suilicient partial pressure oi the gas to at least partially bleach the ilour or other flnelydivided product and then exposing the our or other finely ldivided product while agitated in a finely divided state to the action of asecond gaseous bleaching agent of a similar or diiierent nature than that used in the ilrst bleaching operation, for a sumcient length of time and at a suiliclent partial pressure oifthe gas to completely bleach and mature the flour or other edible iinely divided product.

These and other objects, -as will hereinafter appear, are accomplished by this invention which may be practiced in apparatus shown in the accompanying drawing in which f Figure l is a vertical section through a doubl compartment agitator with suitable seals for the gas: and

Fig. 2 isa transverse section -on the line 2.--12 oi The foregoing ilgures illustrate a type of apparatus for carrying out the present invention. It consists essentially of an agitator having a housthrough this chute.

bearings` carried by the partition housing, the lower shaft I5 being driven by means of a belt I6 and a pulley Il. This shaft in turn has a pulley I8 which drives a pulley I9 on the shaft I4 by means of a belt 20.

' The shaft Il carries a series `of paddles 24 which serve to beat the iiour and to help keep it in suspension in the air. of the upper compartment. This shaft alsocarries a series of propeller blades 25 which cause the our on the partition I I to be moved from left to right as will presently be more fully explained.

Similarly, the shaft I5 is provided with paddles 26 and with-propeller blades 21, the latter, however, being -set reversely to the blades 25 so as to propel the iiour resting on the bottom I Ia from right to left.

Flour is fed to the agitator by means of a chute 80 which is provided with a our seal 3l t'o prevent gas within the compartment I2 from passing up Thus ilour is delivered to the agitator at the left-hand end of the shaft I4 and is propelled tothe right.

The diluted gas for bleaching in the compartment I2 is supplied thereto through a pipe 35 and may be mixed with several times its volume of air in a mixing valve 36 which'may be of any suitable type for this purpose. Gas is lfed to the compartment I3 through a pipe 4u and may be` mixed with a suitable amount of air by means oi a mixing valve 4I.-

` The compartments I2 and I3 are separated by means of a suitable iiour seal 42l which maintains at all times a suitable depth of our at this point so that gas from one compartment will not readily pass to the other. Likewise, a flour seal 43 is provided at the voutlet end of the compartment. I8 to prevent gas therein fromvpassing to the delivery chute 44 by means of which the bleached ilour leaves the agitator.

It will be seen from the foregoing that 'ilour to be bleached .passes down through the chute 30 ing Ill` with aicentral horizontal partition II f dividing the agitatorinto upperv and lower com-v into compartment I2 where it is violently agitated and mixed with the first bleaching gas and is propelled toward the outlet end at the right by means of the propeller blades 425. As the ilour which has thus passed-its' ilrst bleaching operation 1 passes 'the .ilour .seal 42 it is picked up by the propeller blades 2'I on the shaft I5 and moved to the left'. At the same time, the paddles 26- cause Jit to be violently agitated Aso as to bring it intimatay into' contact with the second meachmg gas in the compartment IQ. As it passes from right to left, lt then receives its second bleaching operation and is delivered to the our seal 43 where it passes down the delivery chute M having passed its second bleaching operation. It additional bleaching operationsare desired, one or` added in vertical alignment with ilour seals between adjacent chambers in the manner disclosed.

According to present commercial bleaching processes, nours are bleached and aged in separate stages ofn treatment. For example, the initial treatment is accomplished with gaseous nitrogen trichloride which matures the flour. Nitrogen trichloride, in addition to being a maturing agent, also possesses bleaching properties, but when used'in sumcient amount to obtain a complete commercial color removal, injures the quality of the flour. Therefore, for this reason, nitrogen trichloride is used in an amount not substantially in excess of that required to mature or age the flour. and the necessary additional bleaching is accomplished by .a subsequent treatment with benzoyl peroxide, which has no maturing properties. The process outlined above is time-consuming since benzoyl peroxide is a solid which requires approximately 10 to 20 hours to completely'react with the iiour and benzoyl peroxide is rather expensive.

Our invention is based upon the discovery that the above-mentioned diiiiculties may be obviated by bleaching and maturing our by a process lwhich comprises exposing the ilour or other edible finely divided milled products, while agitated in a iinely divided state, to the action of a gaseous bleaching agent for a sufiicient length of time and at a sumcient partial pressure of 30 the gas to at least partially bleach the our or other iinely divided product and then exposing the flour or other nnely divided product, while agitated in a -finely divided state, to the action of a second gaseous bleaching ag'ent of a similar or different nature than that used in the ilrst .bleaching operation, for a"sufcient length of time and at a suiiicient partial pressure of the gas to complete the bleaching and maturing of 40 flour, when used reagents.

According to the prior art, th'e desired amount the flour or other ediblel nnely divided product. A's-an alternative to the process set forth above, we may mix or blend a stream of flour which has been so treated with another stream of flour which -has also been similarly treated with other gaseous reagents thereby producing a ilour havspecincation and-claims refers to a method of applying gaseous bleaching agents. In multiple bleaching, flour is treated with multiple doses of bleaching reagent. Two vvariations occurwhen the repeated doses consist on the one hand of the same bleaching reagentand oon the other both variations give improved results.

The use of so-called bleaching agents on ilour vhas two basic objectives: l (1) To improvethe color of the flour; and

(2) To improve the baking properties of the flour. The best result would be a combination 'of the two. V In making the above'statement, it is understood that the problem of bleaching varies from v oneA flour to another and that in manyv cases the desired objective would Vbe to improve 4the color of the flour without injuring its baking properties. These objectives have been sought for .a

- number of years in branches of the milling industry. various bleaching reagents 'have been brought out from'time to time and have been tive of' the present invention was toobtain the hand of diiferent reagents. We have found that the chemical name. and formulsf All but #6 are 76l |widespread commercial use.

above improvements in greater degree and at lower costs.

The present bleaching procedures generally used in industry are based almost entirely upon 5 trial and error experiment. This is partly caused by the fact that the mechanism of bleaching and treating flour by so-calied bleaching agents is not fully understood. It is further caused by the fact that experiments necessary for any thor- 10 ough investigation are comparatively expensive.

Various other reagents which have been used occasionally or have been suggested are, for example, as follows: nitrosyl chloride and hydrogen peroxide, as well asv various liquid fatty acid u peroxides. Gaseous Areagents react practically instantaneously with the'ilour, whereas the solid reagents act slowlyv and may require as much as zo Naonfnitrogen trichloride, NCI: and chlorine.

10 to 20 hours to cause substantially all the color removal of which they are capable after1 complete blending has taken place. Theipresent invention is concerned solely with the fast-acting reagents, that is, with the gaseous classification.

As heretofore stated, partial or total elimination of benzoyl peroxide is .a desired objective 35 because the cost of that material isl very high,

lof the active agent. benzoyl peroxide, or from onecent vto three cents per barrel of finished of reagents was determined on a small scale. This quantity was then added to the flour in a 5 suitable single compartment agitator. The gas usually consisted of a single component, for instance, chlorine. According tothe present process, thegase used in bleaching are applied only in compara- 50 tively small quantities and have been diluted with' air tov low partial pressures, say in the order o'f 0.5 to 35 mm. of mercury.

in combination with gaseous For convenience in reference, the bleaching agents herein mentioned are listed showing; both Reagents numbered 1. 3,

gaseous. Reagents considered Chemical name Formula How produced 1 Nitrogen peroxide- NOz,NiO. Generated by vassage f nir over electr c arc. 2 Chlorine dioxide..- C10: May be produced according to the process set forth in U. S. Pat. No. 2,172,434, dated Sept. l2, to rge L Cunm. l Nilgen trichlo- NCI: l l:illcfclzlorlliincvvitiila son ammo um sat. 4 Chlorine.. Ch Elcon lysis of salt-solut 'Hypouummma. noci rrintzh enorme water esone. Benzoyi peroxide.. (0.8.00)501. Reaction between benzo l chloride and a suitab l peroxide.

lando are now the initial carotene content of the flour.

ygrams or ounces perv barrel of ilour.

The ultimate results of bleaching processes must be interpreted in the light of both the color of the our and the quality of the nished product.' Both factors are important although the latter may be considered the ultimate test. Neverth less, color removal may be taken as a definite index of the bleaching efdciency of the new processes for bleaching which are described herein. This is'true because a numerical value can be given to the ilour color by measuring the carotenoid pigment content by suitable means. Flour color is conveniently expressed as parts of carotene per million parts of our. Therefore, a high carotene value means a large amount of yellow color in the our, .while a low carotene4 value means a; greaterpart of the color has been removed. Flour bleached according to our process has a very superior white color which indicates a carotene content of approximately 0.4 to 1.1 parts per million parts of il'our, depending on This carotene content is determined by the naphthaalcohol procedure.

Multiple treatment bf flour with the same' bleaching gas y indicate a more efficient procedure. For example,

laboratory tests according to the prior art might indicate on a given ilour that four grams of nitrogen trichloride per barrel of flour were needed toobtain a suitable bleach. It is customary to express dosages of bleaching reagents in terms or As mentioned above, the gas is applied to the ilour at a low partial pressure by mixing with air and blowing the mixture into the agitator. This treatment would give a certain measurable amount of Multiple lbleaching with. dissimilar gases This phase ofvapplicants invention will be prefaced by the following example of the procedure used.

Bakers patent flour is fed into an agitator (as shown in the drawing) at the' rate of twenty barrels per hour. In the conventional equipment, the flour enters at one end of the agitator and is gradually moved to the other end as a result of the action of a. series of agitating blades 'which keep the ilour in constant motion and keep a part of it in suspension in the free space above the body of the flour.l This our after the bleaching treatment exits at the opposite end of the agitator. Nitrogen trichloride (in this example, a total of two grams per barrel) is introduced into the agitatoriat low partial pressure at the same end at which .the iiour enters. This partial pressure is adjusted to the 'optimum level for the emcient utilization of the chemical bleaching agent by varying the speed of the our through the agitator or by varying the amount of air which Yis introduced into'the agitator.- In our experiments, the reaction between the gaseous bleaching agent and the flour in the rst bleaching compartment is complete but the flour, from the first compartment, has not been bleached to the desired level, as this completion of the bleaching and maturing of the Iiioury occurs in the second bleaching compartment of the agitator after the exposure of the our, in a iinely divided condition, to the action of. the second bleaching gas. 0n leaving the first agitator the flour passes to the second bleaching com-A ever, nitrogen peroxide is added to the second bleaching action. However, we have found that if repeated doses of smaller quantities of-the gaseous bleaching reagent were used, a smaller total quantity of bleaching agent is required for the same total bleaching action. For instance, in

some cases three successive treatments of our with one gram each of nitrogen trichloride per barrel of our accomplished the same result that a single dose of four grams of nitrogen trichloride per barrel of flour would give in terms of color removal. At other times, two successive doses of approximately 1.5 grams each would give the same result. This is of considerable importance because the cost of total reagent used is materially decreased, but it may be even more important because of the possibility of achieving a very interesting and valuable additional result. It is possible to overtreat a flour with a bleaching reagent, both from the standpoint of color, baking properties, and keeping qualities. With the usual methods of applyingbleaching agents, adequate color removal may be accomplished but, with certain types of ours this result cannot be accomplished without sacricing desirable bakfing properties and keeping qualities. Therefore,

may be a decidedly advantageous way of applying the bleaching reagent.

bleaching compartment of the agitator at the rate of approximately 11/2 grams per barrel. In this operation, vthe gases are metered by commercially available equipment and the individual operations are carried out according to normal bleaching procedure.

The partial pressure of the nitrogen trichloride in this example, however, was about one millimeter of mercury andthe partial pressure of nitrogen peroxide was approximately/(2 mm. of Hg. A similar bleaching run was made applying the same quantities of gas in the reverse order. The results of this series of experiments which are illustrative of our .process are given in the following table:

Bleaching action of dz'erent methods of application of gas Comparison of thelast two results illustrated above, shows that the order of application is important. The order listed in the last example, that is, nitrogen trichloride followed by nitrogen peroxide, is the preferred method for bleaching action, from the color removal standpoint.

Some reagents are more emcient in removing color (carotenoid pigments principally) than others. Nitrogen peroxide in this respect is regarded as a Weak reagent and is not used accordins to present bleaching practice as the sole color removing agent, fbecause adequate color removal is not achieved.- Color removal experiments have demonstrated that not all color is removed with equal facility. Thus the initial bleaching action seems to take place most, readily. After each increment of color-removal, the residual color has been more dimcult to remove with the same reagent. In other words, it requires relatively more reagent to Aachieve the last fraction of color removal than the flrst. On this basis, when two reagents like nitrogen trichloride and nitrogen peroxide are applied, the former being a much stronger color removing agent than the latter, it would seem that the weaker reagent nitrogen peroxide should be used first to remove the more easily bleached portion of color. In our experiments, the surprising result was that this was not true, and we have demonstrated that the reverse order is preferable. namely, nitrogen trichloride followed by nitrogen peroxide.

Similar experiments made with combinations of the common gases already listed show that in most'cases there is a preferential orderof application for the attainment of optimum bleaching action. 'I'he order of preference for the gases tested depending upon the desired result to be attained is shown in the following table, but since the mechanism of bleac/hing is not fully known, and since only a few reagents are available, no general Ypattern can be given but instead a preferred order for each pair of reagents has been indicated:

Preferential order of application and bleaching action First gas Second gas NCli+i1our Nori-same flour C13-Miou: NCh-l-ssme ilour Cl|+ilour Clr+same iiour ClOri-iiour NCh-l-same flour HOCH-hour CIOrFsame flour The above table indicates the preferred order of application for maximum color removal and is frequently the order` for optimum maturing action. However, the reverse of the order indicated above is sometimes preferable when optimum baking properties alone are considered. For example. with some fleurs it has been found that nitrogen peroxide followed by nitrogen trichloride resulted in optimum baking properties, but not maximum color removal.

Our researches did not indicate that-there is any preference in order for hypochlorous acid versus chlorine or for hypochlorous acid versus nitrogen trichloride.

As applied'to the bleaching reagentsdisted in this table, it is possible to place them in such an order that the best results are obtained when any one of the gases listed is followed by any one of the reagents listed below it. Such an order with the exceptions noted above is as fol lows:

' Cla-Chlorine HOGl-Hypochlorous acid CIOs-Chlorine dioxide NCla-Nitrogen trichloride Noa-Nitrogen peroxide The value of applicants processes of multiple added to the flour tolgive the rest of the bleach. The amount of benzoyl peroxide used was held to a. minimum because of its high cost. If nitrogen trichloride is used in too great a quantity, the flour is injured, and one or more of the baking characteristics of the flour are not satisfactory. Therefore, the amount that can be used is limited and the cost for benzoyl peroxide increases. v

Nitrogen peroxide is very inexpensive because it is easily generated by the electric arc.- However, when it is added alone in amounts large enough to produce adequate color removal, there is a deiinite tendency for the flour to become rancid.

For these reasons nitrogen peroxide is used commercially for only a part of the color vremoval and is followed usually by benzoyl peroxide to complete the desired color removal.'

It has been found experimentally that little or nothing is gained by mixing nitrogen trichloride and nitrogen peroxide simultaneously in the same agitator. Thus, for example, two grams of nitrogen trichloride applied to a our gave a resultant carotene value of 1.22 p. p. m. When two grams of nitrogen trichloride and 0.75 gram nitrogen peroxide were added simultaneously to the flour the carotene value was likewise 1.22 p. p. m. Thus, the addition of nitrogen peroxide was of no value and did not lead to more color removal. 1

It was discovered by experiment that some unexpected and'valuable results are obtained by selecting a preferred order of treatment, namely,

' when nitrogen trichloride treatment is followed by nitrogen peroxide treatment. A greatercolor bleaching has been stated to a certain extent, j

removal is achieved and improved baking propv erties result, as will be seen by the following example:

Los! Carotene volume 2 grams nitrogen trichloride/bbl. and 1.5 l P. p. m. Cc.

grams N01 added simultaneously 0. 98 2725 2 rams nitrogen trichloride/bbl. followed yl-.gramsNOg 0.78 2855 Unbleached flour .7 2. 20 2825 Further, it has been found that considerable .single treatment had, a result that is frequently advantageous. The advantage resides in the circumstance that bleaching sometimes injures the baking properties of the our and hence the smaller the dosage oi' reagent required for adequate color removal the better, in fact, adequate color removal may be achieved without causing substantial damage to baking properties. In general, these results will be to bleach flour more cheaply andin many cases to improve baking qualities with benefit to the miller. the baker and the ultimate consumer.

Multiple bleaching followed by ,blending In addition to the procedure outlined above, a stream ofilour may be bleached by the successive action of two similar gases or by the successive action of two dissimilar gases and then this flour stream may be blended -with another portion of our which has been treated by the successive action of two bleaching agents toobtain desirable results. This makes it possible to obours alone,` but in order to get an eifect that is of commercial value, it is necessary to increase the benefits by considerable amounts. The results of such a test are given in the following table which shows the scoring of bread baked from flour prepared by various treatmentsof the The particular treatment chosen for a flour dependsnot only on the type of wheat used but also upon the use to which the ilour is to be put. For example, three simple classifications of ilour are as follows: (1) bread flour; (2) cake ilour;

(3) all-purpose or family ilour.

While the present invention has been described with particular reference to the treatment of wheat flour, it will be apparent that the invention is not limited thereto but may also be applied to various other streams of milled products such, for example, as rye.

By the term "bleaching as used in the appended claims, it is intendedto mean what the term means in commercial milling, namely color removal withor without accompanying improvesame lot -of patent flour: ment in the baking properties.

, Csrotene Treatment per barrel oi iiour Crumb color mi) Yghll oo'd ilour 1 Control test-2M grams'oi nitrogen trichlorlde, (LN2 C'c.

oz. benzoyl perox zde; 10 l0 2, 800 0. 80 2 1.75 oz. chlorine, followed by 1.5 grams N0; 10-dull white.-. 10 2,670 0.87 3 3 grams nitrogen tr chloride followed by 1.6 grams NOx. iiidull creamy. 10 2, 655 0. 78 4 Blend 50%, #2, 50% #c 11 10+ 2, 195 o. sa

From the above table it will be noted that the While the invention has beendescribed in devolume of'the bread baked with the blend of #2 and #3 is Just as good as that of bread baked with the control flour in spite of the fact that bread baked with either ot the component parts of the blend showed a very marked decrease in the size of the loaf. In addition,the combination of these two ilours yields a ilnal loaf which has a measuraby improved crumb color and grain. Such v results could not have been predicted but evidently must be attributed to acomplementary action of the treatments on the tlour. It will be noted that the crumb color is graded in units.

The crumb color of a selected standard loaf is taken as 10. The higher number indicates a better color; the rating of 11 is measurably better than 10. When applied to some other ilours of varying grade, the results sometimes are even greater. In this example, the treatment consisted of dividing a given ilour into two parts, treating eachpart with two different gases in succession and then combining the parts after treatment:

Another method of utilizing this same principle is to treat two or more separate iiours with a suitable succession of bleaching gagents and then blend vthe treated fiour;or to treat various groups of nour streams from the same wheat mix with the sameor'ditlerent types of treatments and then to combine these streams to form the tinished products.

of the invention will be apparent to those skilled in the art.

We claim as our invention: Y 1. A process of bleaching flour products nand other nely divided milled cereal products which comprises contacting said: product, while agitated in a tlnely divided state,`=.l with nitrogen trichloride for a time suillcient'to bleach said product partially, and then contactingthe thus partly treated product with nitrogen peroxide to bleach said product further.

2. A process of bleaching our products and other nely divided milled cereal products which comprises contacting said product, while agitated in a ilnely divided state, with nitrogen trichloride for a time sufficient. to bleach said product partially, thereafter contacting the thus partly bleached product, while agitated in a nnely divided state, with nitrogen peroxide for a time sufflcient to bleach said product further, and blending said product with another finely divided milled cereal product treated in the same manner by chlorine followed by nitrogen peroxide.

CHARLES 0. FERRARI. WILIJB B. N. 

